1. Field of the Invention
The invention is related to the field of analog-to-digital conversion, and in particular, to circuitry for multiplexing currents to provide analog-to-digital conversion for multiple parallel voltage signals.
2. Statement of the Problem
Analog-to-Digital (A-D) conversion is a well-known and essential element of electronic signal processing. A-D Converters (ADCs) have been developed to convert analog voltage signals into digital signals with digital values corresponding to the analog voltages. As integrated circuits have developed, the number of analog voltage signals that need A-D conversion has grown, so the number of ADCs in integrated circuits has grown as well. Unfortunately, the growth in ADCs runs counter to the critical need to reduce the area and power requirements in most integrated circuits. To reduce the area and power of integrated circuits, the number of ADCs in an integrated circuit had to be reduced.
High-speed ADCs were developed to solve this problem. In this solution, multiple analog voltage signals are multiplexed together to form a time-interleaved analog voltage signal. The high-speed ADC receives the time-interleaved analog voltage signal and produces a corresponding time-interleaved digital signal. The digital signal from the ADC is de-multiplexed to obtain digital values that correspond to the analog voltages. Thus, multiple analog voltage signals may share a single high-speed ADC, and the number is ADCs is reduced.
It is often necessary to apply gain to an analog voltage signal. The gain increases the strength of the analog voltage signal to improve subsequent signal processing. Often, gain is applied by converting the voltage signal into a corresponding current signal, and then, by converting the current signal back into a corresponding voltage signal that has greater signal strength then the original voltage signal.
There are two basic techniques to combine the above gain and high-speed ADC technologies. The gain may be applied individually to the analog voltage signals before they are multiplexed to form the time-interleaved voltage signal for the ADC. Alternatively, the analog voltage signals may be multiplexed to form the time-interleaved voltage signal, and then, the gain may be applied to the time-interleaved voltage signal. Unfortunately, these solutions can be slow, and they may require increased power and area that may not be cost-effective for the integrated circuit.
The invention helps solve the above problems with an A-D conversion circuit that provides voltage gain and uses a high-speed ADC. Advantageously, the A-D conversion circuit multiplexes the currents that are used to provide the voltage gain. Multiplexing currents can be faster than multiplexing voltages. The A-D conversion circuit can also use less area and power than previous solutions.
Some examples of the invention include an analog-to-digital conversion circuit or its method of operation. The analog-to-digital conversion circuit comprises a voltage-to-current conversion circuit, current multiplexer, current-to-voltage conversion circuit, and an analog-to-digital converter. The voltage-to-current conversion circuit converts parallel analog voltage signals into corresponding parallel analog current signals. The current multiplexer multiplexes the parallel analog current signals into a time-interleaved analog current signal. The current-to-voltage conversion circuit converts the time-interleaved analog current signal into a corresponding time-interleaved analog voltage signal and provides gain for the time-interleaved analog voltage signal. The analog-to-digital converter converts the time-interleaved analog voltage signal into a corresponding digital signal having time-interleaved digital values corresponding to the parallel analog voltage signals.